Method and Reactor for Pyrolysis Conversion of Hydrocarbon Gases

ABSTRACT

A pyrolysis reactor (12) and method for the pyrolysis of hydrocarbon gases (e.g., methane) utilizes a pyrolysis reactor (12) having a unique burner assembly (44) and pyrolysis feed assembly (56) that creates an inwardly spiraling fluid flow pattern of the feed gases to form a swirling gas mixture that passes through a burner conduit (46) with a constricted neck portion or nozzle (52). At least a portion of the swirling gas mixture forms a thin, annular mixed gas flow layer immediately adjacent to the burner conduit (46). A portion of the swirling gas mixture is combusted as the swirling gas mixture passes through the burner conduit (46) and a portion of combustion products circulates in the burner assembly (44). This provides conditions suitable for pyrolysis of hydrocarbons or light alkane gas, such as methane or natural gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. § 371of International PCT Application No. PCT/US2019/021114, filed Mar. 7,2019, which claims the benefit of U.S. Provisional Application No.62/639,577, filed Mar. 7, 2018, each of which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The invention relates to conversion methods for hydrocarbons,particularly alkanes, to pyrolysis products and the reactor design forsuch conversion.

BACKGROUND

The traditional methods of converting lower molecular weightcarbon-containing molecules to higher molecular weights are numerous.The most prevalent methods involve oxidative coupling, partialoxidation, or pyrolysis. Each method has its own benefits and its ownchallenges. High temperature pyrolysis of methane has commonly been usedfor production of acetylene commercially. Depending on the method usedto supply the necessary endothermic heat of pyrolysis, the methaneand/or hydrocarbon pyrolysis to acetylene is broadly categorized intosingle-stage or two-stage processes.

The single-stage method produces acetylene mainly through partialoxidation of methane. A representative single-stage process is thatdeveloped by BASF, which is described in U.S. Pat. No. 5,789,644. Thisprocess has been commercialized at a 50 KTA scale using multiplereactors in Germany and the U.S. In this process, natural gas serves forthe hydrocarbon feed and pure oxygen serves as the oxidant. The twostreams are premixed in a diffuser, and the premixed fuel rich gas isburnt using a burner block through partial oxidation. This processusually operates at atmospheric pressure or slightly elevated pressure,with the volume ratio of oxygen to natural gas at about 0.6. A majordisadvantage of such a design is the flashback risks of the premixedflame under various feedstock and operating conditions, as well as theplurality of burners used, which increases the probability of failure orshutdown of the reactor and also increases the cost of building thereactor.

In two-stage acetylene production, the processes convert methane toacetylene through pyrolysis, using the thermal energy of the hightemperature product gases from complete combustion. Those processesdescribed in British Patent Nos. GB921,305 and GB958,046, U.S. Pat. App.Pub. No. US2005/0065391, and SABIC's U.S. Pat. No. 8,080,697 arerepresentative technologies for such two-stage process. This processcomprises two main reaction zones followed by a quenching zone. Thefirst reaction zone serves as a near stoichiometric combustor to supplythe necessary endothermic heat of hydrocarbon pyrolysis taking place inthe second reaction zone, into which a fresh hydrocarbon feed such asmethane is introduced. In the quenching zone, water or heavy oil is usedas a coolant to cool down instantaneously the hot product gas from thepyrolysis zone. A major disadvantage of such a design is large heatlosses that are incurred in cooling the combustor walls in order toprotect them.

The proposed invention is free from the above-discussed disadvantages ofconventional single- and two-stage processes. It provides a simple,safe, and efficient process of nearly simultaneous mixing, combustion,and pyrolysis. The process is realized by the proposed special designincluding a converging-diverging burner nozzle and disk-like inlets fornearly tangential injection of both hydrocarbon and oxidizer gases.

These improvements are described in more detail next.

SUMMARY

A pyrolysis reactor for the pyrolysis of hydrocarbon gases has apyrolysis reactor vessel having a reactor wall that defines a pyrolysisreaction chamber. A burner assembly of the reactor has a burner conduitwith a circumferential wall that surrounds a central longitudinal axisand extends from opposite upstream and downstream ends of the burnerconduit. The circumferential wall tapers in width from the downstreamand upstream ends to an annular constricted neck portion located betweenthe downstream and upstream ends of the burner conduit. The downstreamend of the burner conduit is in fluid communication with the reactionchamber of the pyrolysis reactor, with the upstream end of the burnerconduit forming a burner assembly inlet.

The pyrolysis reactor further includes a pyrolysis feed assembly influid communication with the burner assembly inlet, with the centralaxis passing through the pyrolysis feed assembly. The feed assembly hasa downstream feed assembly wall that extends circumferentially aroundand joins the upstream end of the burner assembly inlet. The downstreamfeed assembly wall is oriented perpendicular to the central axis. Anupstream feed assembly wall is axially spaced upstream from thedownstream wall along the central axis and extends perpendicularlyacross the central axis. A gas partition wall of the feed assembly isaxially spaced between the downstream and upstream feed assembly wallsand is oriented perpendicular to the central axis and has a centralopening that surrounds the central axis of the burner conduit. Thepartition wall defines an annular hydrocarbon gas inlet flow spacebetween the downstream feed assembly wall and the partition wall and anannular oxygen gas inlet flow space between the partition wall and theupstream feed assembly wall so that hydrocarbon gas feed and oxygen gasfeed are introduced and passed through said flow spaces perpendicularlyto the central axis of the burner conduit in an inwardly spiraling fluidflow pattern within said flow spaces about the central axis of theburner conduit.

The area extending from the central opening of the partition wall to theburner assembly inlet defining a mixing chamber of the pyrolysis feedassembly. Oxygen gas feed from the oxygen gas inlet flow space andhydrocarbon gas feed from the hydrocarbon gas inlet flow space isdischarged into the mixing chamber so that the oxygen and hydrocarbonfeed gases are mixed together and form a swirling gas mixture within themixing chamber, the swirling gas mixture passing through the burnerconduit.

In particular embodiments, at least one of the annular hydrocarbon gasand oxygen gas inlet flow spaces is provided with circumferentiallyspaced apart guide vanes oriented to facilitate the spiraling fluid flowwithin said at least one of the inlet flow spaces. In certainapplications, the guide vanes are movable to selected positions toprovided selected azimuthal-to-radial velocity ratios of each of thelight alkane gas feed stream and the oxygen gas feed stream within theannular inlet flow spaces.

In many embodiments, the reactor wall is cylindrical. In certaininstances, the circumferential wall of the burner conduit from thedownstream end to the annular constricted neck portion, and optionallyan upstream portion of the reactor wall of the pyrolysis reactionchamber that joins the circumferential wall of the burner conduit, isconfigured as a smooth, continuous wall that follows contour lines of anellipsoidal cap or spherical cap shape. The interior of the reactor wallmay be a refractory material in some embodiments.

In a method of converting light alkanes to pyrolysis products, apyrolysis feed is introduced into a pyrolysis reactor. The pyrolysisreactor vessel has a reactor wall that defines a pyrolysis reactionchamber. The reactor further includes a burner assembly having a burnerconduit with a circumferential wall that surrounds a centrallongitudinal axis and extends from opposite upstream and downstream endsof the burner conduit. The circumferential wall has an annularconstricted neck portion located between the downstream and upstreamends of the burner conduit. The downstream end of the burner conduit isin fluid communication with the reaction chamber of the pyrolysisreactor, the upstream end of the burner conduit forming a burnerassembly inlet.

In the method, the reactor further includes a pyrolysis feed assemblyhaving an annular alkane gas flow space and an annular oxygen gas flowspace that discharge into a central mixing chamber that is in fluidcommunication with the burner assembly inlet. An alkane-containing gasfeed stream of the pyrolysis feed is introduced into the annular alkanegas flow space and an oxygen-containing gas feed stream of the pyrolysisfeed is introduced into the annular oxygen gas flow space. The gases areintroduced so that the alkane-containing gas feed stream and theoxygen-containing gas feed stream pass through said flow spacesperpendicularly to the central axis of the burner conduit in an inwardlyspiraling fluid flow pattern within said flow spaces that flows aboutthe central axis of the burner conduit, with the oxygen-containing gasfeed stream from the oxygen gas flow space and alkane-containing gasfeed stream from the alkane gas flow space being discharged into themixing chamber so that the alkane-containing gas and oxygen-containinggas feed streams are mixed together and form a swirling gas mixturewithin the mixing chamber. The swirling gas mixture is allowed to passthrough the burner conduit, with at least a portion of the swirling gasmixture forming a thin, annular mixed gas flow layer immediatelyadjacent to the burner conduit, and wherein a portion of the swirlinggas mixture is combusted as the swirling gas mixture passes through theburner conduit to provide conditions suitable for pyrolysis of the lightalkane gas from the alkane-containing gas feed stream within thepyrolysis reaction chamber of the reactor vessel. A portion of the lightalkane gas is converted to pyrolysis products within the pyrolysisreaction chamber. The pyrolysis products are removed from the reactionchamber of the reactor vessel.

In particular embodiments, a back flow of flue gases is formed withinthe pyrolysis reactor that flows upstream and radially inward from thethin, annular mixed gas flow layer along the central longitudinal axistoward the upstream end of the burner conduit.

In certain applications, the light alkane gas is a methane gas ornatural gas. The methane gas or natural gas (NG) feed and the oxygen gasfeed may be introduced into the pyrolysis feed assembly in a CH₄/O₂ orNG/O₂ molar ratio of from 1 to 5.

Pyrolysis products may be removed from the reaction chamber and bequenched within a quenching unit.

The azimuthal-to-radial velocity ratio of each of the light alkane gasfeed stream and the oxygen gas feed stream within the annular flowspaces may be from 0 to 30.

The light alkane gas feed stream and the oxygen gas feed stream are eachintroduced into the respective annular flow spaces in the samerotational direction.

At least one of the annular hydrocarbon gas and oxygen gas flow spacesis provided with circumferentially spaced apart guide vanes oriented tofacilitate the rotating swirling fluid flow within said at least oneflow spaces. In certain embodiments, the guide vanes may be movable toselected positions to provided selected azimuthal-to-radial velocityratios of each of the light alkane gas feed stream and the oxygen gasfeed stream within the annular flow spaces.

The reactor wall may be cylindrical. And the circumferential wall of theburner conduit from the downstream end to the annular constricted neckportion, and optionally an upstream portion of the reactor wall of thepyrolysis reaction chamber that joins the circumferential wall of theburner conduit, may be configured as a smooth, continuous wall thatfollows contour lines of an ellipsoidal cap or spherical cap shape. Theinterior of the reactor wall may be a refractory material.

The annular alkane gas flow space and the annular oxygen gas flow spacemay be defined by planar walls of the pyrolysis feed assembly that areoriented perpendicular to the central axis of the burner conduit. Theannular alkane gas flow space may be located at a position along thecentral axis downstream from the annular oxygen gas flow space.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments described herein,and the advantages thereof, reference is now made to the followingdescriptions taken in conjunction with the accompanying figures, inwhich:

FIG. 1 is a process flow diagram of a pyrolysis system for convertinghydrocarbon gases, such as methane, into pyrolysis products inaccordance with particular embodiments;

FIG. 2 is a schematic representation of a pyrolysis reactor shown incross section, constructed in accordance with particular embodiments;

FIG. 3 is perspective view of lower portion of the pyrolysis reactor ofFIG. 2, showing a burner assembly and pyrolysis feed gas assemblyconstructed in accordance with particular embodiments;

FIG. 4 is schematic showing the angle of guide vanes of a pyrolysis feedgas assembly of the pyrolysis reactor of FIG. 2 relative to a centrallongitudinal axis of a burner assembly of the reactor, in accordancewith particular embodiments;

FIG. 5 is a schematic of the pyrolysis reactor of FIG. 2 showing gasflows within the reactor;

FIG. 6 is representation of the pyrolysis reactor geometry and velocityvectors showing the direction of gas flow in a lab scale pyrolysisreactor unit model of Example 1;

FIG. 7 is a representation of the temperature distribution of the labscale pyrolysis reactor unit of Example 1;

FIG. 8 is a plot of the temperature profile in relation to the radialdistance from the device axis of a constricted neck portion of a burnerconduit of the lab scale pyrolysis reactor of Example 1, where r_(n) isthe neck radius;

FIG. 9 shows a plot of the axial and swirl velocity in relation to theradial distance from the device axis of a constricted neck portion of aburner conduit of the lab scale pyrolysis reactor of Example 1, wherer_(n) is the neck radius;

FIG. 10 is a representation of mass fraction distribution for oxygen gasof the lab scale pyrolysis reactor unit of Example 1;

FIG. 11 is a representation of mass fraction distribution for acetylene(C₂H₂) of the lab scale pyrolysis reactor unit of Example 1;

FIG. 12 is a 3-dimensional plot of the effect of azimuthal-to-radialvelocity ratios for each of methane and oxygen gas feeds and theresulting yield of acetylene (C₂H₂) in a lab scale pyrolysis reactorunit model of Example 2;

FIG. 13 is a plot of the effect of the methane/O₂ molar feed ratios onpyrolysis performance in a lab scale pyrolysis reactor unit model ofExample 3;

FIG. 14 is a plot of the numerical simulation results summarized as themass flow rate increases for both CH₄ and O₂ while maintaining themethane/oxygen feeding ratio of Example 4; and

FIG. 15 is a plot of the numerical simulation results as all dimensionsof the reactor described herein are uniformly scaled-up, while the flowvelocity is maintained in all cases, for Example 4.

DETAILED DESCRIPTION

In the present disclosure, a novel system is utilized that transforms atwo-stage combustion-pyrolysis process into a single stage. The systemand process utilizes a “combustion and pyrolysis while mixing” concept.This is achieved by utilizing annular highly swirled jets of feed gasand oxygen gas under particular fluid-dynamics that are fed to a uniqueburner assembly of a pyrolysis reactor. Different from the conventionalsingle-stage partial oxidation methods that utilize a premixed flame,the combustion in the present reactor design features a compact flamewith complete combustion from nearly non-premixed gases [i.e., the gasesstart to mix as they meet within a mixing chamber of a feed assembly ofthe reactor] that provide high gas temperatures of up to about 2800° C.The combustion reaction supplies the necessary heat for pyrolysis ofexcess methane gas or other feed gas that is entrained into the hotcombustion gases through the direct contact and recirculation in thesame reaction chamber of the pyrolysis reactor.

It should be noted that throughout the description, although thediscussion and examples presented may relate to the conversion ofmethane to acetylene and other pyrolysis products, the methods andsystems presented may be equally applicable to the conversion of othernon-methane alkane compounds to higher value alkyne compounds or toother hydrocarbons, which may be non-alkane hydrocarbons, into pyrolysisproducts.

Referring to FIG. 1, a pyrolysis system 10 for the pyrolysis of methaneor other hydrocarbons is shown. The system 10 includes a pyrolysisreactor 12, which is described in more detail later on. Anoxygen-containing gas feed stream 14 is fed to the reactor 12. Theoxygen-containing gas feed 14 may be a concentrated oxygen-gas feed,wherein a majority of the feed (i.e., >50 mol %) is composed of oxygengas (O₂). In many instances, the oxygen-containing gas will be ahigh-purity oxygen-containing gas feed composed of O₂ in an amount offrom 20 mol % to 100 mol % of the oxygen gas feed stream. This may bethat provided from an air separation unit (ASU) 16 used for separatingoxygen gas from air or other oxygen-gas source. Air may also be used asthe oxygen-containing gas. In cases where air is used as theoxygen-containing gas, or cases where there are large amounts ofimpurities (e.g., N₂) in the oxygen-containing gas feed, separation ofsuch impurities from the product may be necessary downstream.

A hydrocarbon-containing gas feed stream 18 is fed to the reactor 12separately from the oxygen gas feed stream 14. The feed stream 18 may bea hydrocarbon gas that contains one or more alkanes. These may be lightalkanes such as C₁ to C₆ alkanes. In many embodiments, thehydrocarbon-containing gas feed stream 18 is a methane-containing gasfeed stream. The methane-containing gas feed 18 may be a pure methanegas or may be methane gas source containing other gases. In certaininstance, the feed stream may be predominantly methane (i.e., >50 mol %)or entirely methane. In particular embodiments, the feed stream may becomposed of natural gas (NG), which may have a methane content of from85 mol % to 97 mol % or more, or other hydrocarbon-rich gases. In somecases the feed stream 18 may be a pretreated feed stream that has beentreated to remove undesirable components, such as sulfur-containingcompounds. The feed stream 18 may be preheated prior to being introducedinto the reactor 12. In particular applications, the feed stream 18 maybe heated to a temperature of from 25° C. to 500° C. to improveconversion efficiency or vaporize heavier alkanes. Such preheating mayuse a heat source that is provided partly or entirely from heatgenerated during the pyrolysis reactor because the overall process isexothermic. Alternatively, the preheating heat source may be providedfrom other external sources.

It should be noted in the description, if a numerical value,concentration or range is presented, each numerical value should be readonce as modified by the term “about” (unless already expressly somodified), and then read again as not so modified unless otherwiseindicated in context. Also, in the description, it should be understoodthat an amount range listed or described as being useful, suitable, orthe like, is intended that any and every value within the range,including the end points, is to be considered as having been stated. Forexample, “a range of from 1 to 10” is to be read as indicating each andevery possible number along the continuum between about 1 and about 10.Thus, even if specific points within the range, or even no point withinthe range, are explicitly identified or referred to, it is to beunderstood that the inventor appreciates and understands that any andall points within the range are to be considered to have been specified,and that inventor possesses the entire range and all points within therange.

The stoichiometric ratio for the complete combustion of methane withpure oxygen requires CH₄/O₂ mole ratio of 0.5 according to the followingexothermic reaction (1) below:

CH₄+2O₂→CO₂+2H₂O (−802 kJ/mol CH₄)   (1)

In the present combustion pyrolysis process, a CH₄/O₂ or NG/O₂ (fornatural gas) mole ratio of around 1 to 5 may be used. The excess methaneor NG gas serves as “crack gas.” The crack gas is converted to C₂ and C₃hydrocarbons through endothermic pyrolysis reactions for methane asfollows:

2CH₄→C₂H₂+3H₂ (+188 kJ/mol CH4)   (2)

2CH₄→C₂H₄+2H₂ (+101 kJ/mol CH4)   (3)

2CH₄→C₂H₆+H₂ (+32.5 kJ/mol CH4)   (4)

3CH₄→C₃H₆+3H₂ (+81.6 kJ/mol CH4)   (5)

3CH₄→C₃H₈+2H₂ (+40.2 kJ/mol CH4)   (6)

Due to the highly endothermic nature of the pyrolysis reactions, thecombustion pyrolysis process requires high temperature, usually above1500° C., in order to achieve a high yield of C₂+ hydrocarbons. Thepyrolysis reaction occurs without the presence or need of a catalyst.The thermal energy at this high temperature is supplied by the uniquepyrolysis burner and feed assemblies of the pyrolysis reactor, as isdiscussed in more detail later on.

The pyrolysis product gases 20 may contain C₂+ hydrocarbons, in whichacetylene is the main product, as well as synthesis gas (carbon monoxideand hydrogen). The pyrolysis gases need to be quenched within a fewmilliseconds downstream, typically less than 10 millisecond, in order tominimize the formation of heavy hydrocarbons and soot. This can beachieved by a short residence time in the hot temperature zone of thereactor 12 due to their high velocity, followed by quenching in aquenching unit 22, such as a water-droplet-spray quench vessel, or othersuitable gas quench devices.

The quenched products 24 may be delivered to a separation unit 26, wherethe pyrolysis product gases are separated to form a product stream 28containing a high concentration of acetylene gas (C₂H₂), which can befurther used for various acetylene byproducts using Reppe chemistry orreformed in a hydrogenation unit 30 to produce hydrogenated products,such as ethylene and other products 32. A portion of the separatedpyrolysis process gas 34, which is typically composed of CH₄ and otheralkanes, may be recycled to the pyrolysis reactor 12 for higherconversion and yield performance Synthesis gas 36 may also be separatedin the separation unit 26 from the process gas for chemical productionand power generation usage.

It should be noted that while the system 10 of FIG. 1 shows single unitsfor the various process steps, each unit could be composed of one ormore units that may operate in conjunction with one another, such asparallel or sequentially, to carry out the various process stepsdescribed.

Referring to FIG. 2, an elevational cross-sectional schematicrepresentation of the pyrolysis reactor 12 for pyrolysis of hydrocarbongases, such as methane or natural gas, is shown. The pyrolysis reactor12 includes a reactor vessel 38 having a reactor wall 40 that defines areaction chamber 41. The reactor wall 40 may have a cylindricalconfiguration with a constant diameter along all or a portion of itslength, which may constitute a majority of its length. In mostinstances, the reactor 12 is oriented vertically so that the cylindricalreactor wall 40 is oriented in an upright orientation. The reactor canhave other orientations (e.g., horizontal, sloped, etc.), however,because the process is controlled by the centrifugal force, whichexceeds the gravitational force by a few orders of magnitude. Thereactor vessel 38 may be configured to provide a length to diameterratio (L/D) of at least 2. In particular applications, the L/D ratio mayrange from 2-5.

The reactor vessel 38 may be formed from steel. In certain embodiments,a cooling jacket can be provided around the reactor vessel, wherein asecond steel wall 42 is positioned around and spaced from the innerreactor wall 40 and a cooling fluid, such as water may be circulatedthrough the jacket formed between the walls 40, 42. In otherembodiments, the reactor wall 40 may be formed from one or more layersof refractory material that line the interior of an outer steel wall toreduce heat loss and sustain the high temperatures of the reactor 12. Aswill be described later on, because of the unique design and operationof the reactor 12, the reactor wall 40 is cooled internally by thehigh-velocity near-wall gas flow pushed by centrifugal forces againstthe reactor wall 40 so that in some applications no exterior coolingjacket is required. This also allows refractory materials to be used forthe interior of the reactor wall 40. Refractory materials (withoutcooling) typically cannot be used with conventional pyrolysis reactorsdue to the high heats encountered.

An outlet 43 is provided at the upper or downstream end of the reactorvessel 38 for removing or discharging pyrolysis products from thereaction chamber 41. Although the outlet 43 is shown located at theupper end of the reactor vessel 38, in other embodiments it may belocated at the lower end of the reactor vessel 38, so that the flowthrough the reactor is in the opposite direction (i.e., from top tobottom). The outlet diameter can be same as the diameter of the reactorwall 40 or the outlet diameter may be reduced to accelerate the flowbefore quenching and collection downstream.

The reactor 12 includes a burner assembly 44 that is coupled to thelower or upstream end of the reactor wall 40 of the reactor vessel 38.The burner assembly 44 has a burner conduit 46 with a circumferentialwall 48 that surrounds a central longitudinal axis 50. Where the reactor12 is oriented vertically, the central axis 50 will also be orientedvertically as well and will be concentric with or parallel to a centralvertical axis of the reactor vessel 38. In the embodiment shown, theaxis 50 is concentric with and aligned with the central longitudinalaxis of the reactor vessel 38. The circumferential wall extends fromopposite upstream and downstream ends of the burner conduit 46. As canbe seen in FIG. 2, the circumferential wall 48 smoothly tapers in widthor diameter from the downstream and upstream ends to an annularconstricted neck portion 52 located between the downstream and upstreamends of the burner conduit 46. The interior of the circumferential wall48 may have a circular perpendicular cross section (with respect to theaxis 50) along its length. The circumferential wall 48 interior definesa flow path of the burner assembly 44 with the constricted neck portion52 forming a converging-diverging streamlined nozzle of the burnerassembly 44. The nozzle geometry of the neck portion 52 is configuredbased upon the theory relating to swirling conical jets of a viscousincompressible fluid described in detail later on.

The circumferential wall of the burner conduit from the downstream endwhere it joins reactor wall 40 to the annular constricted neck portion52 may, in some embodiments, be configured as a smooth, continuousconcave wall having an ellipsoidal cap or spherical cap shape orconfiguration. Likewise, the upstream portion of the reactor wall 40 ofthe pyrolysis reaction chamber 41 that joins the circumferential wall ofthe burner conduit may also be configured as a smooth, continuousconcave wall that follow contour lines of an ellipsoidal cap orspherical cap shape or configuration.

The downstream end of the burner conduit 46 joins the reactor wall 40around its perimeter so that the burner conduit 46 is in fluidcommunication with the reactor chamber 41 of the pyrolysis reactorvessel 38. The upstream end of the burner conduit 46 forms a burnerassembly inlet 54.

A pyrolysis feed assembly 56 is provided with the reactor 12. Thepyrolysis feed assembly is in fluid communication with the inlet 54 ofthe burner assembly 44, with the central axis 50 passing through thepyrolysis feed assembly 56. The feed assembly 56 includes a downstreamfeed assembly wall 58 that extends circumferentially around and joinsthe upstream end of the burner assembly inlet 54. The feed assembly wall58 is oriented perpendicularly or substantially perpendicularly (i.e.,≤5 degrees from perpendicular about its circumference) to the centralaxis 50.

Axially spaced upstream from the downstream wall 58 along the centralaxis 50 is an upstream feed assembly wall 60. The upstream wall 60 isperpendicular to or substantially perpendicularly (i.e., ≤5 degrees fromperpendicular about its circumference as it extends from the centralaxis) to the central axis 50 and extends across the central axis 50.

A gas partition wall 62 is axially spaced between the downstream andupstream feed assembly walls 58, 60. The partition wall 62 is alsooriented perpendicularly to or substantially perpendicularly (i.e., ≤5degrees from perpendicular about its circumference as it extends fromthe central axis) to the central axis and has a central opening 64 thatsurrounds the central axis 50 and is concentric with the burner conduit46. The central opening 64 has a circular configuration. Other shapesfor the central opening 64 (e.g., oval) may also be used provided suchconfiguration facilitates the swirling of gases to provide the requiredflow patterns described herein. This shape may also correspond to thecross sectional shape of the circumferential wall 48 of the burnerconduit 46. In most applications, however, the central opening 64 willbe circular in shape. The central opening 64 may have a diameter orwidth that is the same or slightly different than the diameter or widthof the constricted neck 52 of the burner conduit 46 at its narrowestpoint.

The partition wall 62 defines an annular gas flow space 66 locatedbetween the downstream feed assembly wall 58 and the downstream side ofthe partition wall 62. Likewise, an annular gas flow space 68 is definedby the upstream side of the partition wall 62 and the upstream feedassembly wall 60. This provides flow passages through which hydrocarbongas feed to be pyrolyzed (e.g., CH₄ or natural gas) and oxygen gas canbe separately introduced and passed through the flow spaces 66, 68,respectively, perpendicularly or substantially perpendicular to thecentral axis 50 of the burner conduit 46. In most cases, the upper ordownstream flow space 66 will constitute a hydrocarbon gas inlet flowspace for introducing an oxygen-containing gas and the lower or upstreamflow space 68 will constitute an oxygen gas inlet flow space forintroducing an oxygen-containing gas. This configuration enhances mixingsince the centrifugal force presses the higher-density oxygen into thelower-density hydrocarbon (e.g., methane).

The walls 58, 60, and 62 forming the flow spaces 66, 68 are axiallyspaced apart to provide the desired volume and flow characteristics forthe gases flowing therethrough. This may be based upon the desired flowrates or linear velocities of each of the hydrocarbon and oxygen feedgases and their relative amounts. For instance, the relative volume ofoxygen gas needed for the combustion is typically less than that of thehydrocarbon feed gas needed for the combustion and pyrolysis. Therefore,the partition wall 62 may be spaced closer to the upstream wall 60 sothat the hydrocarbon gas flow space 66 is larger to accommodate thegreater flow of hydrocarbon gas.

Annular gas manifolds 70, 72 provided around the periphery of the flowspaces 66, 68 are fluidly coupled to a hydrocarbon-containing-gas sourceand an oxygen-containing-gas source, respectively. The manifolds 70, 72are provided with the pyrolysis feed assembly 56 to facilitateintroduction of feed gases into the flow spaces 66, 68. Gas inlets 74,76 from the manifolds 70, 72 may be directed tangentially into the flowspaces 66, 68 so that the gases are not directed only radially towardthe central axis 50 from the inlets 74, 76, but instead are directedmostly tangentially around the central axis to provide an inwardlyspiraling flow pattern. Furthermore, the walls 58, 60, 62 of the feedgas assembly keep the gases introduced from the manifolds 70, 72 fromflowing axially along the central axis 50 while they are containedwithin the flow spaces 66, 68. The manifolds 70, 72 can be configured asstandard manifolds (e.g., snail-like) as may be typically used in vortexdevices.

Referring to FIG. 3, one or both of the flow spaces 66, 68 may beprovided with a plurality of circumferentially spaced guide vanes 78, 80(e.g., 10 to 60 guide vanes). Each guide vane 78, 80 may be a planarmember that is oriented in a plane that is parallel to the central axisand extends between the walls 58, 60 and the partition wall 62. Theguide vanes 78, 80 may be circumferentially spaced an equal distancefrom one another. In certain embodiments, the guide vanes 78, 80 may befixed in place, with the upper and lower side edges of the guide vanesbeing joined along their lengths or a portion of their lengths to thewalls 58, 60, 62 so that there are no air gaps between the side edges ofthe vanes 78, 80 and the walls 58, 60, 62. In other embodiments,however, the guide vanes are movable. In such cases, the upper and lowerside edges of the vanes 78, 80 may be closely spaced from the walls 58,60, 62 to provide a small clearance to allow such movement but thatminimizes air gaps where gases may pass through. Seals may also be usedto effectively close these spaces or clearances. In other instances, thevanes 78, 80 may be oriented so that the plane of the vane is in anon-parallel or slanted orientation relative to the central axis. Insuch cases, the side edges may be fixed to the walls 58, 60, 63 orremain closely spaced from walls 58, 60, 62 to minimize air gaps forgasses to pass through. In other instances, the guide vanes 78, 80 maybe configured as airfoils having curved surfaces, which may be orientedwith the width being parallel or non-parallel to the axis 50, to providedesired flow characteristics.

The guide vanes 78, 80 are provided adjacent to the outer perimeter ofthe flow spaces 66, 68 and are spaced in an annular or circular ringpattern near the manifold inlets 70, 72, respectively, although they maybe provided in an annular pattern at other positions located radiallyinward or further within the interior of the flow spaces 66, 68, or oneor more additional annular sets of guide vanes may be located radiallyinward from that located along the outer periphery to facilitateinwardly spiraling fluid flow.

Feed gases from the manifolds 70, 72 are delivered nearly tangentiallyto the outer perimeter of the flow spaces 66, 68, where the guide vanes78, 80 further facilitate directing the gas flow in an inwardly swirlingor spiraling fluid flow pattern within the flow spaces 66, 68. In otherembodiments, the guide vanes 78, 80 may impart the full tangential flowof the introduced gases in cases where the gas from inlets 74, 76 may bedirected radially toward the central axis 50. In such cases the guidevanes 78, 80 prevent flow directly toward the central axis 50 and directthe flowing gases tangentially to provide the inwardly swirling orspiraling fluid flow pattern.

The guide vanes 78, 80 of each flow space 70, 72 may be mounted onactuators (not shown) so that they can be selectively movable to variouspositions to provide a selected inwardly spiraling flow pattern. Theguide vanes 78, 80 may be pivotal about an axis that is parallel to thecentral axis 50 so that the vanes 78, 80 may be moved to variouspositions.

The orientation of the vanes 78, 80, as well as the orientation of thetangential inlets 74, 76 may be seen in FIG. 4. As shown, the line 82represents the angle of orientation of the vanes 78, 80 and/or inlets74, 76 with respect to the radial line 84 extending radially from thecentral axis 50. Angle A is the angle between the tangential line 82 andthe radial line 84. In particular embodiments, the angle A may rangefrom 50° to 85°, more typically from 60° to 75°. Thus, the vanes 78, 80may be permanently oriented at an angle A within this range or may bemovable to various angular orientations within this range. In mostcases, each of the vanes 78, 80 within the annular pattern will be setat the same angle A and when actuated will move in unison or close tounison to the same angle A to provide the desired spiraling fluid flowcharacteristics. The angle(s) of orientation A of the vanes 78 and/orinlets 74 of flow passage 66 may be the same or different than theangle(s) of orientation of the vanes 80 or inlets 76 of flow passage 68.

In most cases, the tangential gas inlets 74, 76 and/or the guide vanes78, 80 will be oriented to provide spiraling fluid jet flow that is inthe same rotational direction about the axis 50, i.e., clockwise orcounter-clockwise. Thus, both the hydrocarbon-containing gas and theoxygen-containing gas will both spirally flow clockwise orcounterclockwise about the axis 50 within the flow spaces 66, 68.

Referring again to FIG. 2, the area extending from the central opening64 of the partition wall 62 to the burner assembly inlet 54 define amixing chamber 86 of the pyrolysis feed assembly 56. It is here thatgases from the flow space inlets 66, 68 are discharged and are mixedwithin the mixing chamber 86 to form a swirling gas mixture within themixing chamber 86. This swirling gas mixture then passes through theburner conduit 46 and into the reaction chamber 41 of the reactor vessel38.

As discussed previously, the gas flow space 66 will typically be used tointroduce a spiraling jet of hydrocarbon-containing gas into the mixingchamber 86. This may be an alkane-containing gas, such as methane ornatural gas. The flow space 68, which is located upstream or below theflow space 66, will typically be used to introduce a spiraling jet ofoxygen-containing gas. The hydrocarbon and oxygen gases are introducedseparately from one another into the flow spaces 66, 68 and not asmixture, which could cause safety issues.

As the spiraling jet gases from flow spaces 66, 68 flow radially inward,they are discharged into the mixing chamber 86 where the hydrocarbongases and oxygen gases are mixed. The swirling gas mixture then passesaxially through the burner conduit 46, with at least a portion of theswirling gas mixture forming a thin, annular alkane-rich gas flow layerimmediately adjacent to the burner conduit 46. A portion of the swirlinggas mixture is combusted as the swirling gas mixture passes through theburner conduit to provide conditions suitable for pyrolysis of thehydrocarbon gases, such as methane or light alkane gases, within thepyrolysis reaction chamber 41 of the reactor vessel 38, with a portionof the hydrocarbon gases being converted to pyrolysis products withinthe pyrolysis reaction chamber 41.

The oxygen gas has a higher molecular weight than the methane gas, whichwould be typically used as a pyrolysis feed gas. Furthermore, thehydrocarbon-containing gas is typically preheated, whereas theoxygen-containing gas may not be, so that the methane- or otheralkane-containing gas is less dense or lighter than theoxygen-containing gas. Thus, as the oxygen-containing gas is dischargedas a spiraling jet from flow space 68 it will move into the lighterhydrocarbon-containing gas through the central opening 64 into themixing chamber 86. Centrifugal forces push the jetted oxygen gas intothe surrounding hydrocarbon or methane gas jet. This enhances mixing ofthe two streams. In addition, the hydrocarbon gas from flow space inlet66 and oxygen gas from flow space inlet 68 typically have differentvelocities. This can create a shear layer between the gases that issubject to the Kelvin-Helmholtz instability to further enhance mixing ofthe gases.

Additionally, the oxygen, as it is mixed with the methane or hydrocarbongas, will generally remain encapsulated by a surrounding swirlingportion of the discharged spiraling jet of hydrocarbon gases within thecenter of the mixing chamber 86. The oxygen gas will thus be enclosed orsurrounded by the swirling hydrocarbon gases as it passes through theburner conduit 46. This is due to the fact that the combusted mixture isseveral times lighter than the incoming hydrocarbon gas and thecentrifugal forces push the hydrocarbon gas to the burner/reactor walls(52, 48).

This can be seen schematically in FIG. 5 where the reactor 12 is shown.As shown, methane feed 88 is introduced nearly tangentially into flowspace 66 and oxygen gas 90 is separately introduced nearly tangentiallyinto flow space 68 to create inwardly spiraling jet flow where the gasesmix within the mixing chamber 86. The dashed lines 92, 94 generally showthe overall through-flow path of the methane feed 88 and oxygen 90.

As can be seen in FIG. 5 and FIG. 10 (discussed in more detail lateron), while mixing occurs within the mixing chamber 86, a portion of themethane feed exists as an outer non-mixed layer of swirling methane feed92 that remains exterior to the oxygen flow 94 as it mixes with theremaining methane and passes through the burner assembly 44. At least aportion of the swirling gas mixture forms a thin, annular mixed gas flowlayer immediately adjacent to the burner conduit 46, as can be seen inFIG. 10. A portion of the swirling gas mixture is combusted as theswirling gas mixture passes through the burner conduit 46 to provideconditions suitable for pyrolysis of the hydrocarbon gases, such asmethane or light alkane gases, within the pyrolysis reaction chamber 41of the reactor vessel 38. Such conditions include temperatures of from2700° C. to 2850° C. within the reaction chamber 41, where pyrolysisreactions take place.

As the combustion gases are formed they are at a much highertemperatures (approaching 2850° C.) and will thus be lighter than thecooler incoming pressurized non-combusted hydrocarbon and oxygen gases.The centrifugal forces of the swirling gases provide a stablestratification of density, where the higher-density hydrocarbon gases(e.g., methane), as well as any non-combusted oxygen gases, are pushedas a thin layer 92, 94 towards the sidewall 40 (FIG. 5) of the reactorvessel 38. This occurs while the centrifugal buoyancy pushes the hotflue or combustion gases toward the axis 50. The thermal stratificationwherein the cooler gases are pushed outward as at 92, 94 protects thesidewalls 40 of the reactor vessel 38 from overheating. The devicegeometry and the gas-mixture swirl also result in a back flow ofcombustion or flue gases 96 formed from the combustion of the gasmixture within the reaction chamber 41 that flows upstream and radiallyinward from the thin, annular mixed gas flow layers 92, 94, thatcirculate within the reaction chamber 41, as shown in FIG. 5, to formrecirculation zone 98. This recirculation also forms and stabilizes theburner assembly flame 100 so that it is compact and remains close to thedownstream end of the burner conduit 46, resulting in better andcomplete combustion.

Referring to FIG. 2, in operation, a hydrocarbon-containing gas isintroduced from manifold 70 to tangential inlets 74 into flow space 66.The hydrocarbon-containing gas may be methane, natural gas, light-alkanegases (e.g., C₂-C₆), etc. An oxygen-containing gas, which may be aconcentrated or pure oxygen gas, such as from the air separation unit16, is introduced though manifold 72 through inlets 76 into the flowspace 68. In certain applications, for methane or natural gas (NG), themole ratio of CH₄/O₂ or NG/O₂ may range from 1 to 5, more particularlyfrom 1 to 4, and still more particularly from 1.5 to 2.5, and even stillmore particularly from 1.8 to 2. Such ratio may depend upon theparticular operating conditions and desired products to be formed. Thegas feed streams may be introduced to provide different flow velocitiesto provide the Kelvin-Helmholtz instability for enhanced mixing. Theflow velocities may range from 10 to 500 m/s, more particularly from 100to 400 m/s. The reactor 12 may be operated at from 100 kPa to 20,000kPa, with a gas residence time within the reactor of from 10 to 10,000microseconds.

The gases are introduced and flow through the flow spaces 66, 68 so thatthe axial velocity (i.e., relative to the axis 50) is zero prior tobeing discharged into the mixing chamber 86. The tangential inlets 74,76 and/or the orientation of the guide vanes 78, 80 may be set for eachflow space 66, 68 so that a selected azimuthal-to-radial velocity foreach of the feed streams that flow through the flow spaces 66, 68 isachieved. With respect to the azimuthal-to-radial velocity, inparticular embodiments, this may range from 0 to 30 or more, moreparticularly from 0, 1, or 2 to 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30. Insome applications the azimuthal-to-radial velocity may range from 0 to5, more particularly from 2 to 4. The particular azimuthal-to-radialratio may vary depending upon the particular reactor configuration andcomposition of the hydrocarbon/oxygen streams, however.

Pyrolysis products produced in the reactor are removed from the reactorvessel 38 through outlet 43, where they may be quenched and furtherprocessed and recycled, as discussed with respect to the process stepspreviously described for FIG. 1.

In a variation of the pyrolysis reactor described, additionalhydrocarbon feed gas (e.g., methane, natural gas, etc.) can beintroduced at an intermediate position along the length of reactorvessel, such as at inlet 102 (FIG. 2). One or more such inlets 94 may beprovided at various locations and in the reactor vessel 38, which may becircumferentially and longitudinally spaced apart. The inlets 102 may beoriented or configured so that gases are introduced tangentially, aswell, to facilitate swirling fluid flow, similar to that delivered fromthe feed assembly 56.

In some embodiments, a plurality of burner assemblies and correspondingpyrolysis feed assemblies can be provided in a single reactor whilemaintaining the high performance.

The reactor design described herein features high methane conversion andselectivity, higher overall C₂+ yield than other conventionalsingle-stage or two-stage acetylene production methods. The reactor isrelatively simple in configuration, which significantly reduces thecapital and operating costs. The high-swirling burner provides stableand compact non-premixed combustion, resulting in cooler reactor walltemperatures facilitated by the high-speed annular flow of the methaneadjacent the reactor wall. The reactor can be scaled up by increasingfeeding rate and dimension scale up.

The following examples serve to further illustrate various embodimentsand applications.

EXAMPLES

In the following examples, Computational Fluid Dynamics (CFD)simulations, using commercial software available as the ANSYS FLUENT®software product, were conducted for the optimal design of a pyrolysisreactor, as has been described herein, to verify its performance bynumerical experiments. The swirling fluid flow, heat transfer, anddetailed gas phase reactions were modeled in a two-dimensionalaxisymmetric CFD framework using Reynolds Averaged Navier-Stokes (RANS)approach using Reynolds Stress turbulence model. The modeled base caseANJEVOC-CP reactor has an inner diameter of about 6 inch, with amethane/oxygen molar ratio of 1.8-2.0.

Example 1

FIG. 6 shows the pyrolysis reactor geometry and axial-velocitydistribution in a lab scale unit model. The areas arrow directionindicate flow direction of the gas phase, and its length indicates therelative magnitude of the velocity. At the feed assembly inlet, theaxial velocity is zero, the radial and the azimuthal velocity areuniform and the azimuthal-to-radial velocity ratio is three for both O₂and CH₄. This highly swirling flow forms a recirculation region near theaxis of the reactor as described above in FIG. 5, which stabilizes theflame and enhances the mixing while burning. This backflow (reverse flowregion in reaction chamber near the axis in FIG. 6) presses thecombustion to the nozzle neck. This can be seen in FIG. 7, where thedarker regions downstream from the burner conduit indicate highertemperatures and the lighter regions indicating cooler temperatures. Thebackflow of gases presses the combustion to the burner conduitconstriction in the darker high-temperature region (the maximaltemperature is 2800° C.) depicted as the dark tri-pointed shape in FIG.7 located at and near the burner assembly. It also shows that the hotregion is located near the central axis and the hot combustion gases areseparated from the sidewall of the burner conduit by the thin annularjet (lighter region) layer, which prevents the sidewall fromoverheating.

FIGS. 8 and 9 illustrate the wall protection from overheating by theannular swirling jet in greater detail by showing the radial profiles oftemperature and velocity at the nozzle neck. The maximal temperature,achieved in the combustion region at the axis (r=0), is 3004° K. FIG. 8shows that the temperature drops down to 805° K at the sidewall, wherer=r_(n) (i.e., r/r_(n)=1); r_(n) is the neck radius.

In FIG. 9 the sharp peak of the axial velocity (337 m/s) near thesidewall shows the high-velocity jetting behavior. This high-speedannular jet, transporting the most mass flux of the cooler CH₄, protectsthe sidewall of the reactor from overheating. The jet is pressed to thesidewall by the centrifugal force provided by the high-speed swirlvelocity whose near-sidewall peak is 327 m/s.

FIG. 10 depicts distributions of oxygen and FIG. 11 depicts acetylene(C₂H₂) formation from the pyrolysis of methane in the reactor. In FIG.10, the oxygen concentration is shown at its highest in the flow spaceto the far bottom, upstream from the burner assembly, which appears as adark region within the flow space. From there moving downstream, theoxygen concentration decreases, as shown by the two-pronged forked areaflowing out of the oxygen flow space and directed towards the burnerassembly and the lighter areas emanating from the burner where theoxygen is mixing with methane. The lighter areas in the downstreammethane-containing flow space, the very thin light area along thesidewalls of the burner conduit and along the upstream end of thereactor, as well as the majority of the reaction chamber of the reactordownstream of the burner assembly indicate a lack of oxygen. Thus,oxygen is totally consumed by combustion in the burner assembly, whilethe cylindrical part of the reaction chamber is practically oxygen-free.

In FIG. 11, the lighter areas to the bottom or upstream in the reactornear the burner assembly indicate a low mass fraction of C₂H₂. Thedarker areas to the top or downstream of the reactor indicate anproduction of C₂H₂ concentration from the pyrolysis of methane. As canbe seen when comparing FIGS. 10 and 11, C₂H₂ is absent where O₂ presentsand C₂H₂ is mostly produced in the cylindrical reaction chamber of thereactor. Therefore, the burner assembly serves as a compact non-premixedburner and the cylindrical part of the reactor facilitates pyrolysis.

Example 2

FIG. 12 shows the combined effect of the azimuthal-to-radial velocityratio of the two inlet streams (CH₄ and O₂). The peak yield is achievedwith both streams co-rotating at high azimuthal-to-radial velocity ratioof 3, indicating the high azimuthal-to-radial velocity ratio isfavorable in creating a wide recirculation region and fast mixing.

Example 3

FIG. 13 shows the effect of methane/oxygen mole ratio on the pyrolysisperformance, varying the ratio from 1.6 to 2.4. The sensitivity analysisshows that the overall methane conversion decreases along with theincreasing methane/oxygen ratio, due to the combustion temperature andavailable thermal heat for pyrolysis. On the other hand, the selectivityis slightly increased from a ratio of 1.6 to a ratio of around 2. As aproduct of these two metrics, the overall C₂+ yield finds a peak atratio around 1.8 at this specific scale reaches around 28.2% undercertain operating conditions. It is noteworthy that the optimizedmethane/oxygen ratio may vary under different reactor scale, heat loss,as well as operating pressures.

Example 4

Referring to FIG. 14, the numerical simulation results are summarized asthe mass flow rate increases for both CH₄ and O₂ while maintaining themethane/oxygen feeding ratio. The C₂+ yield slightly increases with thethroughput because of the enhanced mixing effect under increasing Renumber. Shorter residence time may also be favorable for higher C₂+yield if high conversion is not sacrificed. FIG. 15 summarizes thenumerical simulation results as all dimensions of the reactor describedherein are uniformly scaled-up, while the flow velocity is maintained inall cases. Results show that CH₄ conversion, C₂+ yield, and C₂+selectivity remain nearly invariant in this dimension range.

While the invention has been shown in some of its forms, it should beapparent to those skilled in the art that it is not so limited, but issusceptible to various changes and modifications without departing fromthe scope of the invention based on experimental data or otheroptimizations considering the overall economics of the process.Accordingly, it is appropriate that the appended claims be construedbroadly and in a manner consistent with the scope of the invention.

We claim:
 1. A pyrolysis reactor for the pyrolysis of hydrocarbon gasescomprising: a pyrolysis reactor vessel having a reactor wall thatdefines a pyrolysis reaction chamber; a burner assembly having a burnerconduit with a circumferential wall that surrounds a centrallongitudinal axis and extends from opposite upstream and downstream endsof the burner conduit, the circumferential wall tapering in width fromthe downstream and upstream ends to an annular constricted neck portionlocated between the downstream and upstream ends of the burner conduit,the downstream end of the burner conduit being in fluid communicationwith the reaction chamber of the pyrolysis reactor, the upstream end ofthe burner conduit forming a burner assembly inlet; a pyrolysis feedassembly in fluid communication with the burner assembly inlet, with thecentral axis passing through the pyrolysis feed assembly, the feedassembly comprising: a downstream feed assembly wall that extendscircumferentially around and joins the upstream end of the burnerassembly inlet, the downstream feed assembly wall being orientedperpendicular to the central axis; an upstream feed assembly wall thatis axially spaced upstream from the downstream wall along the centralaxis and extends perpendicularly across the central axis; a gaspartition wall axially spaced between the downstream and upstream feedassembly walls that is oriented perpendicular to the central axis andhas a central opening that surrounds the central axis of the burnerconduit, the partition wall defining an annular hydrocarbon gas inletflow space between the downstream feed assembly wall and the partitionwall and an annular oxygen gas inlet flow space between the partitionwall and the upstream feed assembly wall so that hydrocarbon gas feedand oxygen gas feed are introduced and passed through said flow spacesperpendicularly to the central axis of the burner conduit in an inwardlyspiraling fluid flow pattern within said flow spaces about the centralaxis of the burner conduit; and wherein the area extending from thecentral opening of the partition wall to the burner assembly inletdefining a mixing chamber of the pyrolysis feed assembly, with oxygengas feed from the oxygen gas inlet flow space and hydrocarbon gas feedfrom the hydrocarbon gas inlet flow space being discharged into themixing chamber so that the oxygen and hydrocarbon feed gases are mixedtogether and form a swirling gas mixture within the mixing chamber, theswirling gas mixture passing through the burner conduit.
 2. Thepyrolysis reactor of claim 1, wherein: at least one of the annularhydrocarbon gas and oxygen gas inlet flow spaces is provided withcircumferentially spaced apart guide vanes oriented to facilitate thespiraling fluid flow within said at least one the inlet flow spaces. 3.The pyrolysis reactor of claim 2, wherein: the guide vanes are movableto selected positions to provided selected azimuthal-to-radial velocityratios of each of the light alkane gas feed stream and the oxygen gasfeed stream within the annular inlet flow spaces.
 4. The pyrolysisreactor of claim 1, wherein: the reactor wall is cylindrical.
 5. Thepyrolysis reactor of claim 1, wherein: the circumferential wall of theburner conduit from the downstream end to the annular constricted neckportion, and optionally an upstream portion of the reactor wall of thepyrolysis reaction chamber that joins the circumferential wall of theburner conduit, is configured as a smooth, continuous wall that followscontour lines of an ellipsoidal cap or spherical cap shape.
 6. Thepyrolysis reactor of claim 1, wherein: the interior of the reactor wallis a refractory material.
 7. A method of converting light alkanes topyrolysis products, the method comprising: introducing a pyrolysis feedinto a pyrolysis reactor comprising: a pyrolysis reactor vessel having areactor wall that defines a pyrolysis reaction chamber; a burnerassembly having a burner conduit with a circumferential wall thatsurrounds a central longitudinal axis and extends from opposite upstreamand downstream ends of the burner conduit, the circumferential wallhaving an annular constricted neck portion located between thedownstream and upstream ends of the burner conduit, the downstream endof the burner conduit being in fluid communication with the reactionchamber of the pyrolysis reactor, the upstream end of the burner conduitforming a burner assembly inlet; and a pyrolysis feed assembly having anannular alkane gas flow space and an annular oxygen gas flow space thatdischarge into a central mixing chamber that is in fluid communicationwith the burner assembly inlet; introducing an alkane-containing gasfeed stream of the pyrolysis feed into the annular alkane gas flow spaceand an oxygen-containing gas feed stream of the pyrolysis feed into theannular oxygen gas flow space so that the alkane-containing gas feedstream and the oxygen-containing gas feed stream pass through said flowspaces perpendicularly to the central axis of the burner conduit in aninwardly spiraling fluid flow pattern within said flow spaces that flowsabout the central axis of the burner conduit, with the oxygen-containinggas feed stream from the oxygen gas flow space and alkane-containing gasfeed stream from the alkane gas flow space being discharged into themixing chamber so that the alkane-containing gas and oxygen-containinggas feed streams are mixed together and form a swirling gas mixturewithin the mixing chamber; allowing the swirling gas mixture to passthrough the burner conduit, with at least a portion of the swirling gasmixture forming a thin, annular mixed gas flow layer immediatelyadjacent to the burner conduit, and wherein a portion of the swirlinggas mixture is combusted as the swirling gas mixture passes through theburner conduit to provide conditions suitable for pyrolysis of the lightalkane gas from the alkane-containing gas feed stream within thepyrolysis reaction chamber of the reactor vessel, with a portion of thelight alkane gas being converted to pyrolysis products within thepyrolysis reaction chamber; and removing pyrolysis products from thereaction chamber of the reactor vessel.
 8. The method of claim 7,wherein: a back flow of flue gases is formed within the pyrolysisreactor that flows upstream and radially inward from the thin, annularmixed gas flow layer along the central longitudinal axis toward theupstream end of the burner conduit.
 9. The method of claim 7, wherein:the light alkane gas is a methane gas or natural gas.
 10. The method ofclaim 9, wherein: the methane gas or natural gas (NG) feed and theoxygen gas feed are introduced into the pyrolysis feed assembly in aCH₄/O₂ or NG/O₂ molar ratio of from 1 to
 5. 11. The method of claim 7,wherein: pyrolysis products are removed from the reaction chamber andare quenched within a quenching unit.
 12. The method of claim 7,wherein: the azimuthal-to-radial velocity ratio of each of the lightalkane gas feed stream and the oxygen gas feed stream within the annularflow spaces is from 0 to
 30. 13. The method of claim 7, wherein: lightalkane gas feed stream and the oxygen gas feed stream are eachintroduced into the respective annular flow spaces in the samerotational direction.
 14. The method of claim 7, wherein: at least oneof the annular hydrocarbon gas and oxygen gas flow spaces is providedwith circumferentially spaced apart guide vanes oriented to facilitatethe rotating swirling fluid flow within said at least one flow spaces.15. The method of claim 14, wherein: the guide vanes are movable toselected positions to provided selected azimuthal-to-radial velocityratios of each of the light alkane gas feed stream and the oxygen gasfeed stream within the annular flow spaces.
 16. The method of claim 7,wherein: the reactor wall is cylindrical.
 17. The method of claim 7,wherein: the circumferential wall of the burner conduit from thedownstream end to the annular constricted neck portion, and optionallyan upstream portion of the reactor wall of the pyrolysis reactionchamber that joins the circumferential wall of the burner conduit, isconfigured as a smooth, continuous wall that follows contour lines of anellipsoidal cap or spherical cap shape.
 18. The method of claim 7,wherein: the interior of the reactor wall is a refractory material. 19.The method of claim 7, wherein: the annular alkane gas flow space andthe annular oxygen gas flow space are defined by planar walls of thepyrolysis feed assembly that are oriented perpendicular to the centralaxis of the burner conduit.
 20. The method of claim 7, wherein: theannular alkane gas flow space is located at a position along the centralaxis downstream from the annular oxygen gas flow space.